Bleaching and filling leather with amino-sulfonic acid-methylol melamine type resins



Patented Apr. 24, 1951 BLEACHING AND FILLING LEATHER WITH ABHNO-SULFONKC ACID-METHYLOL MEL- AMINE TYPE RESIN S William 0. Dawson, Stamford, *Conn., assignor to American Cyanamid Company, New York, N. Y., a corporation of Maine No Drawing.

Application August 25, 1945,

Serial No. 612,713

4 Claims.

This invention relates to a method of finishing leather by impregnating itwith a novel class of finishing agent having bleaching and filling properties. More particularly, the invention relates to the treatment of vegetable, mineral or resin-tanned leather with water-soluble or waterdispersible finishing compositions containing condensation products of methylol melamines with aminosulfonic acids.

In my Patent No. 2,318,741, dated April 13, 1943, I have shown that methylol melamines are excellent tanning and finishing agents for hides, skins, and leather. I have now discovered that v,-'a'i-er-dispersible products having good bleaching and f ling props ties for leather are obtained when meth dol melamines condensed \idth aminosulionic acid salts. These condensation products form stable aqueous solutions which can be shipped and store-d by the customer without deterioration, and which can be added di rectly to leather finishing processes.

Although the invention in its broader aspects not limited to condensation products of definite structure, I have found that certain welldefined compounds are obtained by condensing monomeric or partially polymerized methylol melamines ccntaining'one or more free methylol groups with water-soluble salts of aminosulfonic acids of the aromatic and aliphatic series, such as sulfanilic acid, metanilic acid, naphthylamine sulfonic acids, and the like. The mechanism of the reaction whereby these compounds are formed and the structure of the condensation products are as follows:

wherein the symbol M represents a methylol melamine, either in the monomeric condition or in a partially polymerized condition, R is the residue of an aminosulfonic acid of the aromatic or aliphatic series and is therefore an aryl or alkylene radical, and X is a salt-forming radical such as sodium, ammonium, ethanolamine, and the like.

Another important feature of the invention resides in the discovery that copolymers of methylol melamines with methylol ureas can be solubilized by condenstaion with the salts of aromatic and aliphatic aminosulfonic acids. This discovery is of importance in the preparation of both tanning and bleaching agents, for the urea-formaldehyde condensation products and particularly dimethylol urea are known to produce white leather of very good appearance.

However, the methylol ureas polymerize so rapidly that they are not well suited for use under commercial tannery conditions. By reacting a methylol urca-methylol melamine cop-olymer with an aminosulfonic acid I have obtained water-soluble compounds that are notprecipitated from solution under practical tannery conditions, and which produce white leather of good appearance. These copolymer condensation products are also good bleaching agents for vegetable or mineral tanned leathers such as chrome leather.

Although compounds of definite compositioncan he obtained by condensing equimolecular quantitias of a methylol melamine and a salt of an aminosulfonic acid, as indicated by the above equation, the invention is not limited to compounds of definite composition. On the contrary, I find that stable solutions possessing tanning, bleaching and filling properties for hides and leathers are obtained when considerably less than the theoretical quantities of aminosulfonic acids are employed. Thus, for example, I have obtained bleaching and filling compositions of good stability by reacting anywhere from 1 to 2 mols of methylol melamine or of a methylol melamine methylol urea copolyiner with 1 mol of aminosulfonic acids, and in some cases the ratio may even be as high as 2.521. By using larger quantities of these com? pounds than those required by theory I have obtained products of improved bleaching and filling properties.

As is noted above, any aminosulfonic acid may be condensed with methylol melamines or with their copolymers with methylol ureas by the above process. Typical compounds of the aliphatic series are taurine (H2N.C2H4.SO3N8.), gamma-aminopropane sulionate (H2N.C3H'1.SO3Na) and beta-aminopropane sulfonate (H2N.CH. (CI-I3) .CHaSOeNa) Aromatic sulfonic acids which may be employed include sulfanilic and orthanilic and metanilic cids, mononuclear polysulfonic acids such as aniline disulfonic acid, polynuclear aromatic monosulfonic acids such as 1-naphthylamine-5- sulfonic acid, and polynuclear aromatic polysulfonic acids such as 2-naphthylamine-5,7- disulfonic acid and 2-naphthylamine-6,8-disulfonic acid. These compounds are preferably employed in the form of their salts, such as the sodium or potassium salts, as noted above. W

The condensation products used in practicing the process of the present invention are preferably obtained by adding an aqueous solution or dispersion of the methylol melamine to a water solution of a water-soluble salt of the aminosulfonic acid followed by heating the mixture at temperatures of about 30 to 100 C., or up to the boiling point of the solution. The reaction product is obtained as a clear, aqueous solution which can be diluted with water to the concentration desired for the tanning or bleaching of leather.

When a composition or improved'stufhng or filling properties is desired it is usually preferable to heat the clear solution of the condensation product at a pH of about 5-7 to promote further polymerization, so that a solution of increased viscoslty is obtained. By polymerizing the condensation product in this manner its filling properties are considerably improved. For greater stability on storage an alkali such as borax or sodium hydroxide is preferably added after the polymerization has been completed in amounts sufficient to raise the pH to about 9-11. The methylol melamine-aminosulfonio acid condensation products may be applied to the leather by any suitable process; however, I prefer to apply them in a tanning drum by the methods described in my earlier patent referred to above. The condensation products are preferably applied to the skins or leather as an aque- Ous solution containing l-l0% of the condensation product, although for special purposes stronger solutions may be employed. Tanning processes requiring complete penetration of the condensation product are usually carried out at relatively high dilutions and for considerably longer periods of time than are bleaching processes in which the principal object is to obtain a lightening of the color of leather which has already been tanned by other processes. After the leather is impregnated with the condensation'product to the desired degree it is usually washed with water and may be fat-liquored and pigmented by any suitable procedure.

The invention will be further illustrated by the following specific examples. It should be understood, however, that these examples are given primarily for purposes of illustration and that the invention in its broader aspects is not limited thereto.

Example 1 To 382 grams of C. P. sulfanilic acid in a 3- necked flask provided with an agitator and thermometer, add 400 grams of water and 450 grams of sodium hydroxide solution. Heat the mixture at -55 C. until a clear solution is obtained. Then ad 252 grams of melamine and 730 grams of 37% formalin. Continue heating until a clear solution results. Add 90 grams of borax or sufficient sodium hydroxide or hydrochloric acid. solution to adjust the pH to approximately 0.0. Dilute with water to 4,450 grams final weight. The resulting solution is stable during shipment and storage and is an excellent bleaching agent for vegetable or chrome tanned leather.

Example 2 To the clear mixture which is obtained after the addition of melamine and formaldehyde in Example 1, there is added a dilute hydrochloric acid solution, prepared by diluting 1 volume of the concentrated acid with 2 volumes of water,

until the pI-l of the reaction mixture is within the range of 6.0-7.0. The mixture is heated at 50-'.0 C. until an appreciable increase in viscosity is observed or to that point at which a definite precipitate is obtained upon addition of 1 ml. of the reaction mixture to 10 ml. of a sodium chloride containing 100 grams of the salt per liter of solution. grams of borax are then added and sufficient water to bring the weight to 4AM; grams, whereupon a stable solution is obtained which has both bleaching and filling properties for chrome tanned leather.

Example 3 To 1'28 grams of sulfanilic acid add 505 grams of water and 250 grams of 20% sodium hydroxide solution. When a clear solution is obtained after treating the mixture at 50 (1., add 252 grams of melamine and 508 grams of formalin. Maintain the temperature at 50-55" C. until the mixture clears, and then treat as described under Example 1 or Example 2. Add 65 grams of borax or sufficient sodium hydroxide to adjust the pH to approximately 9.0 and water to bring the batch to a final weight of 3,285 grams.

Example 4 The melamine and. formalin are mixed in a separate vessel and heated at 50 C. until a clear solution is obtained. This solution is added to the sulfanilic acid-sodium hydroxide solution in Examples 1, 2, and 3, and the mixture then treated as described. A stable solution is obtained which has good bleaching properties.

Example 5 To 126 grams of melamine add 243 grams of formalin and heat at 50 until a clear solution is obtained. Pour this solution into a mixture of 96 grams of sulfanilic acid, 100 grams of 20% sodium hydroxide, and 200 grams of water. The batch may now be finished by the addition of borax and water or acidified with dilute hydrochloric to pH=6.0-7.0 and polymerized as described in Example 2. When polymerization has progressed to the desired degree, add 32 grams of borax or sufiicient sodium hydroxide to adjust the pH to at least 9.0 and add water to make 1,570 grams. The solution is then ready for use as a bleaching agent for vegetable or chrome tanned leather.

Example 6 To 178 grams of sulfanilic acid add 240 grams of water and 215 grams of 20% sodium hydroxide solution. Heat this mixture at 50-55 C. until a clear solution is obtained. To the mixture there is then added 126 grams of melamine, 60 grams of urea and 486 grams of formalin. When the solution is clear, adjust the pH to between 6.0-7.0 with dilute hydrochloric acid. Heat the mixture until a viscous syrup is obtained. Add sufficient sodium hydroxide to adjust the pH to 90-110 and dilute with water to 20% solids.

Example 7 To 106 grams of 1-naphthylamine5-sulfonic acid add 100 grams of 20% sodium hydroxide and 266 grams of water. Heat at EEO-55 C. until a clear solution is obtained. Then add 63 grams of melamine and 142 grams of formalin and continue heating at 50-55 C. until a clear solution is obtained. Now add sufficient dilute hydrochloric acid to adjust the pH to within the range of 6.0-7.0. When the mixture shows a decided increase in viscosity after heating at 50-55 0., add

alkali to adjust the pH to 9.011.0 and dilute with water to 20% solids.

Eazample 8 100 grams of 20% sodium hydroxide and 62.5 grams of taurine are dissolved in 250 grams of water at 50-55 C. To this solution 63 grams of melamine and 142 grams of 37% formalin are added and heating is continued at 50-55 C. until the solution is clear. Dilute hydrochloric acid is then added to bring the pH to 6-7 and heating is continued at the same temperature until the solution shows a decided increase in viscosity. Sodium hydroxide or borax is then added to raise the pH to 9-11 along with sufiicient water to dilute to 20% solids. A clear, stable solution is obtained which has good tanning and bleaching properties.

Example 9 The products of Examples 1, 3, 4 and 5 were applied to chrome retanned side leather by the following procedure. 15 sides (150 pounds) of the leather was washed in a drum for 5 minutes at 100 F. and then drained to 144% moisture and divided into four batches which were placed in tanning drums.

An amount of each of the 20% sulfanilic acidmethylol melamine solutions equal to 10% of the weight of the hides was placed in one of the drums and of water at 100 F. containing 0.25% of NaHCOa, based on the weight of the leather, was added in two feeds 5 minutes apart. Drumming was continued for 45 minutes, after which time the leather was fatliquored and pigmented in the usual manner and horsed up over night. The next day it was set out and dried.

All of the bleach liquors were well exhausted. The leather treated with the product of Example 1 had a much drier surface and was slightly firmer and fuller than in any of the other tests. All the samples had a good white color, and very little color difierence could be noted among them.

Example 10 The condensation products can also be applied to dyed leather by first mixing them with a dye capable of being developed or precipitated in the leather. Thus, for example, chrome tanned, pearled suede goatskins previously dyed by the regular procedure were impregnated by the product of Example 1 by the following procedure.

16 pounds of the colored leather was washed 10 minutes at F. and drained to a short float of water. An amount of logwood equal to 2% of the weight of the leather was dissolved in water and mixed with 3.2 pounds of the 20% solution of Example 1 and the mixture was added to the leather and drummed 15 minutes. 0.5% of copperas, dissolved in Water, was then added and the drumming continued for an additional 15 minutes. A top dye was then applied and the leather was finished in the usual manner. It was fuller and had a better nap than other samples of the same leather to which no condensation product was applied.

It will be noted that the logwood was used to color the methylol melamine-sulfanilic acid condensation product so that its normally white appearance would not discolor the dyed leather. Other dyestuffs can of course be used for the same purpose. The solution of condensation product and dye can also be applied to washed blue stock (i. e. uncolored leather) by the same procedure and the impregnated leather can then be dyed in the usual manner.

What I claim is:

1. A method of bleaching and filling leather which comprises impregnating the leather with an aqueous solution of the polymerized condensation product of 1 mol of an aminosulfonic acid with 1-2.5 mols of a member of the group consisting of methylol melamines and methylol melamine-methylol urea copolymers.

2. A method according to claim 1 in which the aminosulfonic acid is an aromatic aminosulfonic acid.

3. A method according to claim 2 in which the aminosulfonic acid is an aminobenzenesulfonic acid.

4. A method according to claim 3 in which the aminosulfonic acid is sulfanilic acid.

WILLIAM O. DAWSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

1. A METHOD OF BLEACHING AND FILLING LEATHER WHICH COMPRISES IMPREGNATING THE LEATHER WITH AND AQUEOUS SOLUTION OF THE POLYMERIZED CONDENSATION PRODUCT OF 1 MOL OF AN AMINOSULFONIC ACID WITH 1-2.5 MOLS OF A MEMBER OF THE GROUP CONSISTING OF METHYLOL MELAMINES AND METHYLOL MELAMINE-METHYLOL UREA COPOLYMERES. 